Anything but gambling I guess!
You can earn money with money then convert money to
BTC 
I think gambling is not the best way to earn money because gambling its not good. You must claim faucet or joined a signature campaign to earn free bitcoin no need to invest just you have to do is apply a sig campaign and make a post so its very simple to earn bitcoin.
i agree with you that gambling is not good way to earn money and gambling is too risky and that your opinion is best that join a signature to earn free bitcoin in little amount and i think that trading of bitcoin is also good way for earning bitcoin .
Gambling is not the way to earn more bitcoins, it's a good way to lose more bitcoins. If you want to earn you need to do jobs.
or make sure you can hold for a longer time.